The present invention relates generally to antennas, and more specifically to multiple-band antennas that are particularly suited for use in wireless mobile communication devices, such as personal digital assistants, cellular telephones, and wireless two-way email communication devices.
Different types of wireless mobile communication devices, such as personal digital assistants, cellular telephones, and wireless two-way email communication apparatus are available. Many of these devices are intended to be easily carried on the person of a user, often fitting in a shirt or coat pocket.
The antenna configuration of a mobile communication device can significantly affect the overall size or footprint of the device. For example, cellular telephones typically have antenna structures that support communication in multiple operating frequency bands. Various types of antennas for mobile devices are used, such as helical, “inverted F”, folded dipole, and retractable antenna structures, for example. Helical and retractable antennas are typically installed outside a mobile device, and inverted F antennas are usually located inside of a case or housing of a device. Generally, internal antennas are often used instead of external antennas for mobile communication devices for mechanical and ergonomic reasons. Internal antennas are protected by the case or housing of the mobile device and therefore tend to be more durable than external antennas. External antennas also may physically interfere with the surroundings of a mobile device and make a mobile device difficult to use, particularly in limited-space environments.
In some types of mobile communication devices, however, known internal structures and design techniques provide relatively poor communication signal radiation and reception, at least in certain operating positions. One of the biggest challenges for mobile device design is to ensure that the antenna operates effectively for various applications, which determines antenna position related to human support frame. Typical operating positions of a mobile device include, for example, a data input position, in which the mobile device is held in one or both hands, such as when a user is entering a telephone number or email message; a voice communication position, in which the mobile device may be held next to a user's head and a speaker and microphone are used to carry on a conversation; and a “set down” position, in which the mobile device is not in use by the user and is set down on a surface, placed in a holder, or held in or on some other storage apparatus. In these positions, parts of a user's support frame and other ambient objects can block the antenna and degrade its performance. Known internal antennas, that are embedded in the device housing, tend to perform relatively poorly, particularly when a mobile device is in a voice communication position. Although the mobile device is not actively being employed by the user when in the set down position, the antenna should still be functional at least receive communication signals.
The desire to maintain the configuration of the mobile communication device to a size that conveniently fits into a hand of the user, presents a challenge to antenna design. This creates a tradeoff between the antenna performance, which dictates a relatively larger size, and the available space for the antenna within the device.
The antenna size versus performance design issue becomes an even bigger challenge when the handheld communication device, which already must operate in multiple frequency bands, is required to accommodate the additional 700 MHz band. A conventional antenna for operation in that frequency range would entail a physical length of about a quarter of a wavelength, which at 700 MHz is approximately 10.7 cm. To accommodate an antenna with such size inside the handheld device is neither feasible nor practical. Moreover, having a single internal antenna that operates in the existing frequency bands, such as GSM/800/900/1800/1900 and UMTS 2100 in addition to the 700 MHz band, presents a design challenge.